Due to the complexity and variation of soil conditions, soils properties change substantially between treatment subsections, where, accordingly, water contents and coefficient of permeability vary significantly. However, consistent post-treatment technical requirements are wanted between subsections. High Vacuum Densification Method (HVDM, No. ZL01127046.2) and Soft Soil Treatment Using Innovative High Vacuum and Inter-Moderated Compactions (Publication No. CN1624250 A) are two fast soft soil treatment methods.
HVDM inserts vacuum pipes with layered matrix form into soils, imparts vacuum efforts, and densifies the soils using several cycles of vibrations and dynamic compactions. The goal is to decrease the soil water contents, increase the soil compactions and bearing capacities, and mitigate the post-treatment settlements. Construction flow in details is presented in CN Patent No. ZL01127046.2. Notwithstanding HVDM saves lots of time, this method has drawbacks, which have been described and resolved in Soft Soil Treatment Using Innovative High Vacuum and Inter-Moderated Compactions.
The method, Soft Soil Treatment Using Innovative High Vacuum and Inter-Moderated Compactions, treats soils based on the soil water contents and coefficient of permeability by installing vacuum pipes, imparting vacuum effort, uninstalling partial vacuum pipes and imparting vacuum-compaction efforts. Densify the site by dynamic or vibration compaction with varied energies each cycle. Several cycles of combined efforts of vacuum dewatering and inter-moderated compaction are imparted on different soils. Such manner results in decreased water contents, improved compactions and increased bearing capacities.
As partial vacuum pipes are uninstalled, the remained pipes are able to monitor the drainage volume, and thus the magnitude of pore water pressures. The pore water pressures are caused by the compaction energies. In turn, the drainage volume is able to reflect the propriety of compaction energies imparted, namely, the drainage volume of remained pipes will tail off with too high or too low energy imparted. Furthermore, the soft soils are further drained by the pressure gradient caused by the excess pore water pressure (a positive pressure) and the vacuum effort (a negative pressure). However, the following drawbacks exist.
1. As the soft soil treatment scope is vast, the soil properties vary significantly. After treatments, the soil improvements are not consistent, which may result in differential settlements, such as roads' heave-up.
2. The above methods have considered leaving partial vacuum pipes, measuring the water flow volumes and estimating the tamping energies. However, water flows of each soil layer vary significantly and can not be monitored for complicated sites. Different soil layers vary with respect to pipe spacing, vacuum duration. Such drawbacks may lead to spring or rubber soils.
3. In the above methods, groundwater may seepage into the treatment sites, which result to the less guaranteed treatment quality along the treatment boundary.
4. General soft soils are weak. In such cases, aggregates are backfilled in the top to support heavy machineries. However, cost is increased and environment is threatened.